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Part Number: UCC28051
We know that UCC28051 need to be operated at 25W to 100W.
May I know that what it will happen if we use it at 4W to 20W?
And we want to find a part that could support from 4W to 100W at Vout 400V.
Do you have any recommendation?
The UCC28051 will work down to 0W. However, the PFC and THD will decrease at light loads due to crossover distortion.
One thing that you need to do is have the UCC28051 being biased by a separate supply and not an aux winding of the PFC.
There is a 100W EVM that you can order at the following link. There is THD an PF data from 25W to 100W and it is powered from an aux winding.
You can make prediction on THD and PFC at lighter loads based on the THD and PF curves.
I would suggest that you order this EVM and rather than powering it off the ZCD winding. I would power VCC with separate bias supply.
The UCC28051 does not have purposely designed in burst mode. However, when the load drops down near zero the controller will start bursting because there is limitation on how small of a peak current the device can control. Due to offset I believe the minimum peak current is around 75 mV.
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In reply to Mike O':
Thanks for your detail explanation.
I still have some question about this.
1. Could we give VCC a separate supply by a ACDC output 15V with the same ground?
2. How should we do to the ZCD circuit and aux winding of the PFC? Directly remove it or you have a suggestion to this.
3. In the EVM datasheet you provided, what is the spec of L2? We couldn't find this part by internet. Is 800uH/ 2A enough?
In reply to Cindy Chang:
The UCC28051 needs an aux winding on the flyback inductor to work correctly. You can power the VCC of a separate bias supply as well.
To power up the design with a separate bias supply disconnect the diode on the aux winding and you connect the anode to your separate bias.
If you don't need trickle charge startup on the UCC38051 you can remove the resistor from VCC to the output of the bridge rectifier.
I found the data sheet for the PFC boost inductor with aux winding that was used in the EVM and I have attached it for your reference. It actually was a 1 mH inductor and not 800 uH.
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